Prayer... structure (including a dedicated bedtime for the child)... wine... babysitter... love letters/notes... flirting, even if by text... be creative even though you are exhausted! Personally, I nap while my son naps so I can have a last bit of energy left when my hubby comes home later at night. It's not easy and it takes work but remember the spouse/partner is the one who suffers the most in this whole trajectory! Good luck!
I'm not sure this is a tip, but I know that sometimes we have to plan a "date night". Sometimes, you just have to squeeze in a little spontaneous time...which can be interrupted if there is a meltdown or panic attack. Either way, we know our love for each other doesn't change and we find a way...even through our exhaustion to find a little time for each other.
Write love letters while you're in the waiting room during therapies. Send flirty text messages. Do that chore your partner hates. Teach the kids that a closed door means knocking AND hearing an answer before entering. Go to bed early. Take a shower together. Rub your partner's feet. Send the kids out with their grandparents (or other trusted adults) to the movies and take a long walk, hop into bed or just talk and reconnect. Every day, tell him or her that you love them AND why.
Time away from the daily grind. A few hours every week (at least) where the main topic of discussion is not the child(ren). A time to remember and feel the reason you got together originally. A bit of fun; conversations with adults that has nothing to do with ASD. Take some time to express the love that has a way of getting buried and forgotten. Remember your own needs, and those of your spouse.
Humor and sarcasm ;)