Well, here are my thoughts....
First, if you had an opportunity to host a college student from another country while your second child was an infant/toddler, and knew that during those four years, your second child would essentially have the opportunity to become bilingual (but your first child, being say, 5, and in school, would not be at that same 'spongelike' point linguistically) -- would you be doing a disservice to your first child, by providing that opportunity to your second?
You tried to breastfeed your first child. It's not like you sat down and decided that your first child somehow didn't deserve that effort (and you put a lot of effort into it!). If you're able to breastfeed a second child, to whatever goal you set - then your first child will SEE you breastfeeding a sibling, and have that knowledge in place as a parent later in life. I have a good friend with six children. She didn't breastfeed her first because she didn't know anyone who did (early 90's here). She breastfed her last three children - 10 months, 18 months, and 13 months. She told me she does feel guilty that she didn't know more and didn't 'try harder' to breastfeed (she had a bad LC experience with #3 and stopped immediately) ... but she's glad she could breastfeed the other three, and the older three have seen it and it's been normalized for them. And she knows that she did the best she could with the information and support she had at the time.
In terms of how awful breastfeeding was with your first child - I don't recall the exact situation, and I don't think you want me to try to troubleshoot for you anyway.

But each mother/child dyad is different ... maybe it's because the mother is starting out with more information or support, or is more relaxed; maybe that baby just has a better initial latch (those first latches can be so crucial!). I'm trying to think of an analogy ... perhaps someone who was in a really bad, unhealthy romantic relationship?? Because that guy was a stalker doesn't mean that every subsequent guy will be a stalker, too -- it's a good idea to figure out how it happened, but it doesn't mean that the perfectly nice guy your friend sets you up with, won't be Prince Charming, KWIM? And it doesn't mean that you're not capable of having a healthy, happy relationship. I'm not saying your first child was a stalker- but that obviously your breastfeeding relationship was not good.
If it's the same problems all over again when breastfeeding a second child - then you've already BTDT. You recognize what's happening, and you make the decision about what is best for you and your baby at that time. This means that if, say, what you're dealing with is a congenital low supply issue (say, PCOS related) -- then you can decide whether you want to nurse and supplement, or whether it would be better for your situation to move to formula, or donated breastmilk, or whatever. With SJ, we'd already talked through what we'd do if she ended up having reflux, allergies, and me with a supply issue again ... we were ready to supplement with Neocate if we had to. And I went on my Elimination Diet before she was even born just to be preventive.
When dd1 was hospitalized for FTT, and I was told to exclusively pump while she was given Neocate -- we discovered that my supply had diminished to less than 10 oz/day. If it had ever been 'that' high, since part of our problem was a small bit of retained placenta which wasn't discovered until more than 2 months postpartum. I was really lucky to have an LC who caught that, and an OB who humored me by checking (he didn't think it was possible). It wasn't affecting my health at all ... 'just' my supply. It was really a perfect storm of issues .... Ina couldn't gain weight because she couldn't absorb proteins due to her multiple allergies and reflux .... she started limiting feeds to manage her reflux pain .... I don't like to think about those days. The thing is, my LC told me "breastfed babies can't have allergies to things their mothers eat." If I'd been relying just on her, I'd have never eliminated foods, and Ina would have been fully FTT and onto Neocate; I'd have spent the rest of my life thinking she'd been allergic to my milk. Our Ped is the one who talked me through elimination dieting - but she didn't think retained placenta would do anything to my supply.

If I'd been relying on either one of them alone (or if they'd been as ill-informed as some HCPs I read about) I would undoubtedly have been told that our latch issues and our weight gain issues etc. all meant in the end that obviously breastfeeding wasn't for us.
Anyway, I think that is more of my story than you wanted to hear.

Suffice it to say, when dd1 was hospitalized, I would have fed her bear lard (and killed the bear myself to get it for her), if that's what we were told she needed. I was literally afraid she was going to die.
With SJ, as I saw 'normal' breastfed baby poops, an a non-refluxy baby not fighting allergies ... a completely different nursing relationship ... I did a lot of mourning for what Ina and I had missed. Grief over things I'd thought were 'normal baby stuff' with Ina in the early days, and had really been signs of how she was suffering. It wasn't always easy and dh and I both had some good cries over it. But in the end it was a healing thing for me. I still regret that I didn't know enough about Elimination Dieting when we had our troubles with Ina; I still second-guess that maybe if I'd known about Total Elimination Diets, Ina's reflux and allergies might not have cascaded to the point where she couldn't digest any proteins at all for awhile and necessitated hospitalization; if I hadn't been so scared and sleep-deprived, I would have been pumping and supplementing differently. I even feel guilty about the decision we made to put her on 100% Neocate and not give her any of the milk I was pumping during the months I was rebuilding my supply (I was scared her latch issue would turn into a complete bottle preference if she figured out she could get the Good Stuff from a bottle instead of me). That's about 4 months of her life that most of her nutrition (except what she got at breast) was formula-based. I don't know if I did the right thing there in the end ....
The thing is, in the end, we can't give each of our children exactly the same things and experiences and opportunities. We're different people and different parents with each child, based on all the experiences our other child(ren) give us, the opportunities (or lack thereof) we have in our lives/careers, etc. The love is a constant - but everything else necessarily will differ, in good ways and bad. Isn't there an old saying, children are like pancakes, the first one is just for practice?

Ina taught us all sorts of things that we were able to do better with SJ from the beginning (we were adamantly opposed to cosleeping, for instance, and Ina worked on that with great determination for MONTHS until we gave in

) ....
HTH! While we were able to return to breastfeeding with Ina, we were scarred enough from all we went through in her first 1 1/2 years of life that we really weren't ready to think about another child until she was past two years of age. If you had asked me, at 18 months, I probably would have said that we might adopt instead, we were both that scarred by what we'd gone through.