Boyfriend and Ex

So my boyfriend's ex is still kind of involved in his life and it annoys me. He says it's a complicated situation because they were friends before they started dating. We are all Christian and my boyfriend and his ex kind of went for these prayers with this other family before they broke up and after the broke up they still continued to go, it didn't bother me until I found out that he was the one driving her there and back which is like an hour drive so I was like nah that ain't happening. He kind of got angry because to him they are just prayers and it's not like they are going for a joy ride (in his words) Now his ex has a birthday party going on, and she wants my boyfriend to be the MC at the party, I asked him why he agreed and he said he had no option because the family they used to pray with asked him to do so. Am I overreacting or his ex's involvement in his life is just too much.