Why is he acting soo weird?! Please Help!?

Ok, so im 13 years old and my tennis coach is 23 years old, he has been my coach for about 2 years now and hes kind of like my friend etc. He's almost like a brother to my family and always helps out and he comes to my house to play wii with me and my bro all the time and sometimes he goes out to dinner with my fam. i have lessons with him almost everyday and he's like a big brother to me! Well...lately hes been acting really weird. He's been flirting with girls i play tennis with and then look at me, showing off, trying to impress etc, talking about all the workouts he does and subtly trying to show me his muscles and stuff (like lifting up his sleeve randomly) , always smiling at me, mentions all his girlfriends to me, putting his arm around me and by back numerous times for no reason, he also said he had a dream that he was moving into my house with me family, and some other stuff like that! So im just trying to think this through, he is 10 years older than me, so its soooo weird and its just getting freaky and awkward when im around him..it used to be fun and exciting, ya know? Your opinions? Thanks! :)