I don't know if any of the kind people who have participated in this discussion are still looking at this group, but I have done some research on the subject and have found out more.
Firstly, in my particular case there are some specific issues; one is that my son's mother's reluctance to disclose anything at all about her boyfriend to me is considered generally very odd and some kind of control issue she may have. There is a lot in her background that might lead to this conclusion. However, such personal details are unlikely to be of value to any of you.
More pertinent are the issues that pertain to the child. My son, if I've not mentioned it yet, is 2.5 yrs old. He is apparently shortly going to enter an "Oedipal" phase of development where he will form an intense loving bond with his mother. That she brings in a boyfriend could effect the child's development by placing another a competing source for her affection into his life. Consequently, it is important that the boyfriend is introduced in a controlled manner, slowly and deliberately. There are all kinds of issues that swirl around this stage of development; the potential as stated for a sense of competitive loss; importance of only introducing lovers to the child who are firmly established, committed relationships lest the the relationship breaks up and the child, having established a bond, suffers loss at the end of the relationship;
The second component then is the management by the mother of the relationship with me, the father. Despite concerns of privacy, as distinct from secrecy, our son would have been better served had his mother told me that she was involved in a relationship, intended to introduce our son to the boyfriend, and had asked for my support in aiding our son to understand this change. Instead, his mother kept secret the developing events from me, and put our son in the position of messenger i.e. being the one to tell me of the relationship... a role places a heavy burden on him that negatively impacts his development. The child understands the verbal and non-verbal cues that result from my being ambushed by his disclosure to me of his mother's relationship and consequently is confused by the negative reaction.
One could think of his parents not as being divorced "from" each other, but divorced "to" each other from the child's perspective; that to develop effectively, the child is better served by being presented with a unified parental environment, that although his parents are not living together, there is cooperation and consistency in their parenting regime. This should extend to the smaller things in his life, like sleeping patterns/times, toilet training, teeth cleaning, etc., but also to the profound changes in his life like the introduction of his parents' new lovers.
There is a lot more I have learned, but don't want to bore you all! In sum though, cooperation between the parents is highly desirable and conflict should be avoided. The child's health and wellbeing are best served through cooperative parenting. Unfortunately, my personal issue is that my son's mother continues to refuse to tell me anything about her boyfriend except for his first name (and this I learned through my son), refuses to go to a counselor with me to coordinate this and other issues that inevitably will arise in the future, and appears intent on parenting our son according to her own value beliefs based on her unique, and very damaged, psychological background, instead of learning with me through reading and counseling of ways to improve our child's development and eliminate the damaging biases we all carry with us from our own history.
Is anyone still awake now?!