He might start liking them or she might come onto him.
Most Helpful Guy
You have to ask yourself why you worry about him liking them or them coming onto him. From a relationship coaching lens, I must say, this is a confidence problem in yourself. If you were confident in yourself, you wouldn't worry about these two things. So whether you are with this guy or someone else down the road, if you don't fix your confidence, you will forever battle this issue.1
Most Helpful Girl
If you start a relationship with MIGHTS and WHAT IFS , you are not having a healthy and stable relationship, you will ruin this relationship, if YOU DON'T TRUST HIM, then HE MUST EARN YOUR TRUST...
You guys should talk about this, my boyfriend has many female friends, and honestly , I LOVE IT, i don't mind at all, and I TRUST HIM.. and if you show him that you are self secure he will find it EVEN HOTTER so those girls have no chance on you ;)
Just trust me and don't exaggerate, give it a chance, get to know those females, show him that YOU HAVE CHARACTER and that YOU ARE NOT SCARED... ;)