Most Helpful Guy
Wait, first of all, how do you know they're random? If they are random like totally outta the blue then something is up. But maybe she's just a friend and liking is just liking, nothing much really. Unless you see some frequent activity of him following up every posts of other girls then that's something too. If you feel unsure or anything just tell him what you're feeling, you are his girlfriend, you shouldn't be afraid to tell your opinion cuz your opinion should matter more than anyone else's to him. If he shows negative response then he might not be the right guy.
Most Helpful Girl
He's checking other girls. Urgh! Guys are always like that. They've got a girlfriend and still not enough!