Consider the ethical and legal implications before getting married because it is an open-ended legal contract and locks you into a relationship, instead of respecting your freedom to love without pressure. Relationships without non-negotiable legal and behavioural expectations are more sustainable and engender real trust by welcoming honesty and transparency instead of shutting-down important conversations. Above all,ask yourself whether being married might result in feeling possessed, restricted and locked-in instead of having your ongoing freedoms respected and celebrated by the other? Having the option of walking away means you both need to continue working on the connection for it to endure - that is what commitment looks like.
Ensure you do things because you need and/or desire them to lead a meaningful life, including employment and relationships. Too many of us spend our lives trying to convince ourselves and others that we have no choice but to continue doing what we are currently. Start with small steps towards more meaningful stuff and see what transpires; I now have the T-shirt.
Be sex-positive and seek to love yourself and you body. If you don't love yourself then how can you persuade others to? If you are not sex-positive then you will judge the sexual needs/desires of others. Share all of your sexual fantasies with lovers and they may share theirs too - this is the only route to exploration, bonding and satisfaction together. Homo Sapiens is an instinctively socially-sexual species, as is the Bonobo primate. If your partner can't or won't even try, then leave them for someone who will.
Don't trust others based upon your own ethics - assume the worst until proven wrong.
If you are unethical then you will never trust anyone anyhow so just stop it now if you want to be happy.
Never voluntarily engage with NHS Mental Health Services and, if you are unfortunate enough to have them contact you because someone has bad intentions, do not act in a way that might give them the false impression you are unwell instead of frustrated, angry and anxious. Stay calm and breath deeply. Like the police, NHS Mental Health Services are under-resourced, politically-driven and primarily interested in drugging you. They will not spend time listening to you and if they knee-jerk to the conclusion you have a condition, you are royally screwed.
Never assume that the policing and legal systems will apply the law properly or deliver justice for you.
If you are unfortunate enough to have dark skin and/or a foreign name then assume even worse in all of the above situations.
My ground-breaking set of principles for maintaining sustainable relationships