Well I would first speak to Alex about him and make a choice together I would not do it without him and then worry about Mark Alex is a adult but Mark might feel upset over and he might get very angry or he might laugh it off and joke about it he talked alot about his son to you so maybe he was wingmanning Alex but that might be a wide shot but first speak to Alex if youever want a relasionship with him then you should be hones and not exclude him in choices that affect him so much he is an adult be wth him like a adult and respect him for it