Maybe I'm completely wrong here, but he doesn't sound like the best person to be talking to you. My GP has some experience with mental health and related training, but he frequently triggers me - it's not his fault, but I wouldn't go to a brain surgeon for a heart transplant. Therapy is a very difficult thing to get right even for therapists, doctors frequently miss the mark and often cause more harm than good - even when their intentions are good. You need to request some more specialised help. You don't need to believe everything your doctor says if he's wrong - his qualifications aren't more accurate than your feelings. I know this can be hard.
I hope s/he hasn't given you this idea that you would become addicted to more frequent appointments or that having casual sex means you are using someone. I think that it is possible for casual sex to be just that, using the help of another person to help you both relieve sexual tension. Yes it can be harmful in many different circumstances for both you and the other person but unless you are deliberately putting yourself in harms way or actively hurting others, there is nothing wrong with it. It sounds like he thinks perhaps you have borderline personality disorder which actually needs a psychiatrist to diagnose, so referring you to the mental health services should be something he's thinking about anyway. If it's not because of borderline, maybe he frowns upon casual sex?
For PTSD and Borderline therapy is the recommended treatment, DBT is preferred for Borderline and EMDR and CBT is preferred for PTSD, usually however it's not so clearly divided and you will see a therapist who uses many different approaches. The biggest issue is the long waiting times, which often need to be chased up to get started. So really, the sooner you put your name down for this the better. For depression and anxiety, usually shorter 8-12 week CBT styled therapy is offered. But also see if there are any local charities, these may charge something (usually income related, so if you are unemployed a pound per session) but may offer shorter waiting times, longer therapy windows and other advantages.
As for frequent therapy sessions, a stable element in your life may be just what you need and even if you were reliant on it for a time, that's not necessarily a bad thing if it's helping you. Your therapist would prepare you for the end of your therapy, where you often go on a therapy holiday and have more in the future if you need it. It's natural for you to get better and then slip and put what you've learned from therapy to practice, but if you are in a bad place again and need more support to get more then. Having something good for some time and then not having it, is still better than not ever having had anything. For me, my weekly therapy keeps being extended, because I still need the support, also I have a social worker that visits me at home every fortnight to check on how I'm doing and a Psychiatrist for medications and diagnosis help. It took a long time to get the help I needed in the first place and I was hospitalised along the way, which sadly sped up the help I was entitled to, though it should not have been that way. You should be able to ask your doctor for a referral to the local mental health unit for more specialised support and/or therapy.
