It's interesting, in spite of being very amusing. The cliche of a son not finding anyone to live up to their mother's standards might not be so far from the truth. The connection you have with you family can't be explained.
When I was a kid, my best friends mum was a social worker, and had worked with a man and woman who were madly in love as they fought a court case to stay together. Why the court case? They met at a party as adults. Bam. Instant attraction, they wanted to get married and have kids. The problem? They were (biological) brother and sister, and had been brought up separately in care, and that was the first time they had properly met.
I found this interesting, as I know I have a bond with my brother that can't be explained. However, as we grew up together any thought of anything dirty is "Ewww!

". But I have a similar feeling about friends I've known since I was a kid. One of my best friends I've known longer than my brother (he's my age) and any thought of getting it on with him (although he's very attractive, funny and successful) also leaves me cold, because he feels like my brother (no pun intended

).
So, I wonder if, like the brother and sister mentioned above, when the usual growing up together bit is taken away, either by people growing up separately, or by 're-meeting' on the internet, that the bond you have with a family member is as strong as in real life, but free from the taboos that are built in to avoid incest. When you (as a boy) have been brought up by your mum (and you have had a reasonably good relationship), it's presumably natural that you then look for a partner who will continue to look after you in a similar fashion to your mum. So who better to choose than...your mum!