Too possessive ?

My so wants to go to Mexico to build houses for a charity with his dad, however I feel uncomfortable him going without me, but I can't go with him atm. I feel like his dad (who is going with him) wants his son (my so) to not get "tied down" so quickly. This makes me feel he may encourage him to cheat or whatever while he's in the other country. Also my so idolizes his dad alot so it worries me that he'll get influenced. Also, his dad has a big history of cheating on women. What should I do?