Of course he does. I am not saying romantic feelings, those are unlikely, but no one drops 5 years of their lives and the mother of their kid without at least some regret and fond memories. With a child in the picture, he is going to have a lot of regrets.
Not of being with you, but of the break-up in general. There will be additional guilt too – he’ll feel guilty that he is not paying you 100% attention, when he knows he should be.
They split up, remember. And, unless my math is particularly bad today, he had 6 months or so after the break-up to hook back up with her, before he started seeing you.
You shouldn’t be wasting your time in trying to compare yourself to her – you are different people with different things to offer. You have your own relationship with him now. Concentrate on that and stop trying to let his previous relationship define how you behave wth him. Keep it romantic. Keep him interested. Send some love letters of your own! And be his rock. Guys need that too, though most hate like fury to admit it..
Talk it over with him. That can be a bit of a delicate topic to introduce, but it is worth doing, or at least trying. I’d suggest that you talk about it, not in terms of how it makes you feel, but in terms of how you can keep having a good, satisfying relationship and still encourage him to be a good father to his child.