IF SINGLE:
Breaking dates
Not keeping in touch with you during the week (usually a guy you are dating will ask you out for the weekend)
Always out with his buddies
Not interested in what you have to say
Doesn't bother to ask what is going on in your life
Isn't interested in your friends
Is lethargic, moody when with you
Doesn't remember your birthday or other special occasions
MARRIED:
The smell of perfume
Check for lipstick on especially his shirts
Calls in the evening and the person hangs up
Phone #'s your husband has and he doesn't explain whose they are
You can always check his emails or any boards he is on online
Receipts from hotels or motels
Keep an eye on your Visa card for any transactions for jewelry, motels, hotels, rented vehicles, etc.
Working more over-time than he use too
Forgetting your birthday or anniversary (some men can forget and it doesn't mean they are cheating, but they will make up for it.)
Not interested in any aspect of your life such as how your day went, if you want to go out for an evening or have friends over.
A lack of interest in you, or having your friends over for a nice evening
Never taking you out for dinner or a movie
These are but a few, but usually, if most women have a gut instinct follow through on it, but be warned, be sure you have proof and don't be the over-zealous type (or over jealous) and ruin your relationship.
Before you jump to conclusions it's type you both brushed up on your communication skills. So sit down one night and have a nice quiet chat and discuss your relationship.
Good luck Marcy