It's pretty simple really to tell a man is in love. He just treats you a certain way that you know you are a priority in his life. A man in love, when it comes to you he acts a certain way or does certain things he might not ordinarily do.
Its a sign a man is in love when he steps outside of his routine to accommodate you. Maybe he stays up later than normal to talk to you. He may be a night owl, but all of a sudden he goes to bed early like you do. Maybe he hates sappy movies but watches them anyway because you want to. In other words a man in love will be uncomfortable so that you will be comfortable.
If a man wants to see you regardless. Regardless if you have hovered over the toilet all night sick as a dog. He wants to see you regardless if you just crawled out of bed with no make up, in a tee shirt that has food stains all down the front. If your man wants to see you even at your worst, it's a good sign he is in love.
Has your man surprised you lately? Has he brought you a little gift, even if it's something silly like your favorite soda from the corner pantry. Has he brought you flowers or a flower? Maybe he surprised you with a candy bar, taking you to lunch when he usually works clear across town. A sign a man is in love gives to you in little ways.
A man in love talks openly in terms of "we" and does so in front of others. If he is saying we to you that is one thing, but when he does it in front of his friends and coworkers it's a sign he is in love. It's like it is perfectly natural for him when the word "we" escapes his lips.
Another sign a man is in love is he projects into the future. He talks about the things you will be doing together. Perhaps he mentions his vacation and how this year you will be included. Maybe he just mentions a concert a month or so down the road. You can bet if a man if talking about you and him in the future, he is considering you long term.
It's simple really, a man in love acts like he adores you.