From your pre-posting questionnaire, I can see that you are 32 and you were dating this other guy who is 34 for only three weeks. You guys broke up because his 22 year old ex-girlfriend learned she was pregnant, and it is probably your ex’s baby, so he has moved in with her, and is going to try and make a family with her and the baby. The only good thing in all this is that the two of you were only dating for three weeks. I’m sure you’re upset about this, but can you imagine if this happened after three years?! Three weeks is a pretty small time investment in a relationship, so if you look at this from another angle, you’re lucky that it’s a super short term relationship failure, and not a more painful, long-term commitment. 😉
That said, the less you see your ex, the sooner you’ll get over the break up. Remaining “best friends” isn’t going to work for you, and I don’t think you should even try that. You’re not friends — you are exes from a romantic relationship. It’s too difficult to make that work now that he’s rejected you and moved on with his pregnant ex, and is trying to make himself feel better by keeping you in his game. Because of your history together friendship is not a good solution. So make the break clean and move on. It will hurt for a while, but you’ll feel single, soon enough and you’ll find someone new to date.
Hope that helps!