I am not sure I totally understand the question when you say, “stand up for yourself.” It sounds like you are being pressured towards marriage but you are not interested/ready for marriage.

This sounds like simple honest communication. Tell your boyfriend/girlfriend you are not interested in marriage. If you are not sensing the relationship could lead towards marriage, I do not encourage you to stay with it just so you are not alone. Since marriage is the next step, it appears the relationship has existed a long time. If your boyfriend/girlfriend is looking for a relationship that leads to marriage, it is not fair to stay in a relationship with them if you do not want marriage.

The second part of the question makes me wonder if you are maintaining the relationship for the pleasures of intimacy. If you don’t plan on the relationship moving forward, why fan the flames of sexual passion? The Bible tells us to keep sexual intimacy to a minimum outside of marriage.

The Bible tells us how to treat others outside of marriage.

...younger men as brothers, older women as mothers, younger women as sisters, in all purity. 1 Timothy 5:1–2 (ESV)

While this sounds prudish, studies tell us:

• The more intimate a couple is before marriage, the more it diminishes their ability to deal with important conflict issues that should be resolved before their marriage.

• The more sexual partners someone has before their wedding night, the less sexually satisfied they are in their marriage.