First I’ll give you the orthodox take. At the end my own unorthodox take.
It is not a sin in itself, not intrinsically sinful. Thus as with anything else not intrinsically sinful, it would be sinful, neutral, or laudatory according to the right judgment of prudence (wisdom).
Unquestionably it gives scandal to some people. But giving scandal isn’t necessarily sinful. Most of our actions will scandalize at least some people. Deliberately giving scandal with an aim to leading others to sin would be evil. Likewise knowingly giving scandal needlessly (i.e. imprudently) would be a sin too. Being affectionate in a chaste way with your girlfriend is something of great value so that would not be a case of needlessly giving scandal. The more relevant issue is how needlessly tempting of a situation it would be for you or her. If that’s not an issue for you or her, then it wouldn’t IMO be a sin. Scandal and a sin known as “adulation” as well as “seduction” would arise however if you were to pretend to others that you were having sex with her, of course.
I am not ruining my girlfriends reputation.
This is an issue of charity for your gf. However again more than her reputation, chaste affection and time spent together is something of value. That is not to say it necessarily doesn’t come with dangers as I’ve already mentioned. (Also note that these dangers may also correspond to health dangers which can occur even without intercourse and even with the use of a condom, not to mention the risk of pregnancy and the moral temptation that may afford you or her and health risk it may additionally entail regardless of the choice she makes since pregnancy itself introduces health risks to the woman)
No I am not going to move out, it is my apartment and I would not tell her to leave either. I don’t want opinions, I want some facts.
I think people are not understanding the bottom line behind scandal and occasion of sin. The bottom line is a cost-benefit analysis with different elements weighted according to how you would rightly value them. So for example, even if you were chaste and so forth, if you had a little brother who wouldn’t be so successful as you and he were encouraged by your action to do as you do and he gave in to temptation, then that’s a possibility to consider. Ultimately however, in orthdox Catholic ethics here’s what they would say:
The nearer an occasion of sin and/or the greater the potential for leading others on a path to sin, the greater importance or value being pursued must be to justify the situation.
If you have been sleeping with your gf for a long while and you both have remained chaste for the most part, then that’s a point in favor of doing as you do. OTOH, if this has just been a few days, then you really won’t know how good you will be at resisting temptation until later.
NOW: my own opinion
If you truly love her and her, you, it should not be a problem. Also, IMO you should only sleep in the same bed if you wouldn’t regret having had intercourse should that end up happening. If you aren’t at that stage in your relationship, then IMO, in our culture it is not fitting to be in the same bed except maybe just occasionally. Additionally, I would recommend speaking with your doctor and her, hers, so that you might elect to follow their advice in terms of any eventualities or present things (remember it’s not just intercourse that can spread disease; some disease can be spread just through kissing or even holding hands in certain circumstances)