Toddler friends

I have a friend who has a toddler 4 months older than my son. They used to love playing together, but recently my son has been hesitant playing with her. When she comes over he gets really clingy and seems to want to do activities on his own and he gets really frustrated when she tries to play with him. She tends to be more rough and push/ bump into him a lot. (My son has also been pushing his 7 month old sister a lot.) I don’t know if this is just a phase or if it’s something I should be worried about. My son is just over two and not yet talking much, but he understands a lot. They’ve been friends for over a year and I want to try to keep it going. Any advice on how to handle it?