Am i unreasonably jealous?

Imagi

This is a long post so i apologize in advance, but i need help.

So here's what's bothering me. My boyfriend and I have known each other for years but we didn't see each other for a few of those years. When we did meet up again we started dating immediately. Our chemistry is amazing and I know he does love me. However , in October his ex fiancée\baby mama came back and he broke up with me for 2 months. She was using him for money which he found out after she dumped him and started dating another guy.

Flash forward to now. There's this chick that he studies with for history class. She's closer to his age ( he's 42 I'm 29) and when we got back together after the exfiancee fiasco, she got upset that he wouldn't sleep with her even tho were dating and he told her he's loyal. So upset that she unfriended and blocked him on facebook.

Well she friended him again a couple weeks ago and he picked her up from school to go to McDonald's one day. She posted a pick of them in the Jeep, she was in my seat (which yeah it IS the passenger seat) the top was down and she talked about going topless "Jeep only!!!"

The one time I've seen this chick was at the place where my boyfriend and I worked. I came in from break and he was talking to him. I walked 5 feet turned back to ten to say hi and shed already disappeared.

He's given me absolutely no reason to doubt his faithfulness, but it'd her I don't trust or like.

I'm not a jealous girl, he's friendly,charming and attractive so the ladies love him.

So I guess what I want to know is, is it unreasonable or irrational of me to ask him to stop being friends with her? I've never asked anyone to do something like this be fore.