Hi, I'd like to help you with your question.
If you are suspicious, then there is probably good reason to think something is going on. Your girlfriend should not be texting another man while she is with you. In a committed relationship, the only relationship a person should have with the opposite sex is one that their partner is fully aware of and is involved in as well. In other words, she should not be talking to this other man without your full knowledge and consent.
The first thing you should do is sit down with your girlfriend and get the truth. Tell her that her behavior is suspicious and she needs to be honest with you for your relationship to work. Then see what she says. If you feel she is honest with you, then work it out from there. If you feel she is being dishonest with you, you may want to consider ending the relationship. If she is cheating now and lying about it, your relationship will not improve unless she sees a problem with what she is doing.
You may also want to consider not living together anymore and just dating. See where your relationship goes from there. If she is faithful and wants to be with you, she will make an effort to work it out with you. If not, you will know by how she responds.
I hope this helps you,Kate
Thank you for the additional information. It helps.
I have to agree with your family and friends. And you have seen her behavior with your own eyes as well. This is not how someone in a committed relationship acts.
It is very hard to let go of a relationship you felt had a future and that you were committed to. You made an effort to keep it together and she has not. Trust is the basis for a good relationship and if you have lost your trust in your girlfriend, it will be hard to get it back unless she is willing to see her behavior as a problem and work on it.
You may want to have her move out and see how living apart affects your relationship. It may help her see she misses you or it may confirm what you suspect, she is cheating.
If you chose to let the relationship go, allow yourself time to mourn. It is a loss and it will hurt. Get as much support as you feel you need. Give yourself time most of all, at least 6 to 9 months. If you find after this time you cannot let go, seek the help of a therapist.