How should I feel about this?

So me and my boyfriend share a phone. So he was logged on to his Facebook and his ex started messaging him. Well he was telling me that she wanted to come pick him up so they could hang out. But he said he wasn't going to. So they keep texting (he's telling what they're saying) but then he tells me that I should talk to her and become her friend. I told him no cause I think its weird being friends with his ex. What do y'all think about it?