Of course your feelings are natural, esp. with such a young kid.
Looking back, I think the thing that really kept me from feeling the way you do (my ex and I broke up when our twins were 2) was my best friend's mother. My best friend's parents got divorced shortly after I met her, in grade school. Her mother was absolutely awesome. She set high standards for her kids, didn't put up with any disrespect, made everyone toe the line. She had to put up with a lot of crap from her ex. She made decent money, but was very committed to savings and lived frugally as heck, no matter how much her kids complained. But she was happy, confident, competent at EVERYTHING, fun, loving, affectionate. Her kids KNEW they were loved. And she did it all on her own. In general, if she gave advice about anything, as we were growing up, I just assumed she was right.
One thing I noticed - and she discussed openly - was that she always had fun when her kids were with their dad. She indulged a few of her passions, most notably sailing, which she did every other weekend, weather permitting (and that wasn't the type of thing she ordinarily spent money on). The kids needed time with their dad and she was a better parent if she got time to do things she enjoyed, with her adult friends. She needed that time even more, if she was doing everything on her own when the kids were with her. But she had to make the choice to actually get out and do things while the kids were gone, instead of sitting home and missing them. So she did.
I had that idea rattling around in the back of my mind years before I became a single parent, so it was easy to pull it out, dust it off and put it to work. It may take longer for it to sink in, for you. But trust that it's a good policy. Behave as though you believe it, until you really do.
I didn't always go out and do things, when my kids were with their dad. I grew up in a big, Catholic family, so I find it positively luxurious to have snatches of time all by myself in a quiet house. Sometimes I just hung out in my PJs, listened to NPR instead of Barney, took a bubble bath, read a book, got take-out food as a treat. But it IS important not to have ALL your time be alone, no matter your temperament. And if you can't stay home alone without feeling sad, you MUST get yourself out of the house. If you don't have people to hang out with now, join a book club, a hiking club, a group at church. Volunteer somewhere. Give yourself some structure in which it's possible to meet people and let it happen.
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