It sounds like you are burned out by the relationship. She wants to take things more slowly from now on, even if you don't. Marriage won't fix any of these problems.

It's important to have respect for each other. You should respect her choice to stay at home, and she should also respect your need to go out and have fun. You need to find a balance so she can spend time with you alone and so you can do what you want without feeling dragged down.

Think about what she's done for you. What has she given up to come live with you? Does she respect you and your needs? How will a breakup affect her?

Think about yourself. Are you happy being with her? Is she still special to you? How has the rest of the relationship been? How do you think married life with her will work out? What can you say about the new girl that your girlfriend can't give you?

You should also tell her about the new girl you've met. She needs to know how you feel and that she could actually lose you. If she's still unwilling to change or compromise, she's not worth it.

It's a shame losing a 6 year relationship, but you should never feel obliged to stay in it if you don't feel happy or satisfied. Hopefully you two can work it out. If not, go have fun.

(Never had a girlfriend so take this advice with a grain of salt)