Hi Lostindependent3, welcome here.
I'm no good at shorthand so I don't know what LDR is. But anyway.
Even couples without any mental illness at all have fluid relationships due to moods and such, created by the stresses of life, the workloads, the weather, financial pressure and the like. So with your situation this fluidity would be present but more so. This presents a few problems in that your ages are working against you. As much as you love each other 2x 18 year olds the forces of general life can mean that long term success with your lives together is low.
What are the factors that give me this view? Well we are only talking age (maturity) so the factors effecting this are- impatience, over reaction, careers, family pressures, workplace locations, country or origin (in your case), infidelity. Listening to this might be hard but, the facts are clear that two young 18yo's would be more vulnerable to these aspects than say a couple in their 40's.
That doesn't mean it cant be tried. In fact I'd like to see you and your partner try. You may need guidance in the form of counselling when any one of the above stresses present themselves. Sometimes the obvious (in terms of answers to a dispute) are not seen as clear as when they come about in older people, so a third party could a be a welcomed move when you both see positive results. Effectively I'm saying you need to both be wise and wisdom at your age is in its infancy.
Your partner said some beautiful words to you, words that....well I would not ignore...in fact I'd cradle that close to my heart and print it and frame it. Hang it on a wall. You certainly need patience. So what can you do about that?
Well, patience is not available in supermarkets. I needed lots when I was young. In fact when I reached 43yo I thought I had ADHD and got treatment. It was mania I had. Impatience is within you and hard to curb. However mind diversion like hobbies, sports, friends chatting etc (read busy busy busy) will help. When you are down and thinking about him you will need to master the change of mind direction technique...basically short circuiting your sadness to force a mood change.
Important- anything that occurs that you have no power to change is not worth your mind time, if you keep stewing over things it means worrying and worry produces nothing but negativity.
Time is your final clarifier. If in doubt, wait, keep busy and wait. All this will make you wiser.
Good luck Tony WK